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darbydog Author

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Capacity of time machine disk

What size disk is needed for time machine backup

Posted on May 23, 2022 4:47 AM

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rkaufmann87

Level 10

149,622 points

Posted on May 23, 2022 7:37 AM

To clarify it should be 2-3 x the size of how much is stored on the iMac. For example if the iMac has a 1TB drive but only 500 GB of data is on it then get a 1.5 - 3 TB External Hard Disk. If you don't know how much is on the iMac check About this Mac and then if you have external HD;s attached add those up too.

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All Time Machine backups take too long 2018 Mac mini running macOS 12.6.1. I have an 8TB USB drive connected to the machine with two volumes on APFS. One volume I use to Time Machine backup my laptop over the network, and that seems to work just fine. The other volume is a local Time Machine volume for the mini. This is a fairly new disk and it was all working fine for a couple of weeks, but now the local backup takes forever and seems to find hundreds of thousands of files to backup. It takes over 24 hours to complete. Then the next time Time Machine starts, it all happens again, hundreds of thousands of changes found and it runs for 24+ hours. It's almost like the mini doesn't recognize that it only has to do an incremental backup. I know for sure there aren't all that many changes between each backup run. I've double checked the Excludes From Backup options and that all looks reasonable (it excludes both the local and remote TM volumes, iCloud, OneDrive, and Dropbox folders). I can't find anything else that would include so much changes. It estimates the size of a full backup at 1.68TB which appears to be the entire Macintosh HD (303.64GB available of 2TB). I can't find any other settings that would cause TM to do a full backup every single time and I've rebooted the machine at least once to see if that fixes the problem, to no avail. I can't upgrade this machine to Ventura yet due to compatibility issues. Any ideas what's going on or what to look for?
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rkaufmann87

Level 10

149,622 points

May 23, 2022 7:37 AM in response to darbydog

dialabrain

Level 10

138,595 points

May 23, 2022 4:58 AM in response to darbydog

2 to 3 times the size of the internal drive is recommended.

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Capacity of time machine disk